At a Glance

Why Get Tested?

To detect and monitor muscle damage; to help diagnose conditions associated with muscle damage; sometimes to help determine if you have had a heart attack, although for heart attack detection, this test has been largely replaced by troponin

Sample Required?

A blood sample drawn from a vein in your arm

Test Preparation Needed?

None

The Test Sample

What is being tested?

This test measures the amount of creatine kinase (CK) in the blood. Creatine kinase is an enzyme found in the heart, brain, skeletal muscle, and other tissues. Increased amounts of CK are released into the blood when there is muscle damage.

The small amount of CK that is normally in the blood comes primarily from skeletal muscles. Any condition that causes muscle damage and/or interferes with muscle energy production or use can cause an increase in CK. For example, inflammation of muscles, called myositis, can increase CK. Rhabdomyolysis, a breakdown of skeletal muscle tissue, is associated with significantly elevated levels of CK.

Any drug or toxin that interferes with muscle energy production or increases energy requirements

Damage to muscles, such as the heart damage that occurs during a heart attack, can cause increased CK levels within a few hours. Levels peak within 12 to 24 hours and then return to normal within 2 to 4 days. If additional damage occurs or it is ongoing, then CK levels may stay elevated. This fact makes the CK test potentially useful for monitoring for continuing heart or other muscle damage.

Is any test preparation needed to ensure the quality of the sample?

The Test

How is it used?

A creatine kinase (CK) test may be used to detect inflammation of muscles (myositis) or serious muscle damage and/or to diagnose rhabdomyolysis if a person has signs and symptoms, such as muscle weakness, muscle aches, and dark urine. The urine may be dark because of the presence of myoglobin, another substance released by damaged muscles that can be harmful to the kidneys. CK may be ordered by itself or along with other blood chemistry tests such as electrolytes, BUN or creatinine (to evaluate kidney function). A urine myoglobin may also be ordered.

A person may have muscle injury with few or nonspecific symptoms, such as weakness, fever, and nausea, that may also be seen with a variety of other conditions. A health practitioner may use a CK test to help detect muscle damage in these cases, especially if someone is taking a drug such as a statin, using ethanol or cocaine, or has been exposed to a known toxin that has been linked with potential muscle damage. In those who have experienced physical trauma, a CK test may sometimes be used to evaluate and monitor muscle damage.

The CK test may be ordered if a person has chest pain or other symptoms that lead a doctor to suspect heart damage. This assay was once one of the primary tests ordered to help diagnose a heart attack, but in the U.S., this use of CK has been largely replaced by troponin. The CK test may sometimes be used to help detect a second heart attack that occurs shortly after the first.

A series of CK tests may be used to monitor muscle damage, including heart damage, to see if it resolves or continues. If a CK is elevated and the location of the muscle damage is unclear, then a health practitioner may order CK isoenzymes or a CK-MB as follow-up tests, to distinguish between the three types (isoenzymes) of CK: CK-MB (found primarily in heart muscle), CK-MM (found primarily in skeletal muscle), and CK-BB (found primarily in the brain; when present in the blood, it is primarily from smooth muscles, including those in intestines, uterus or placenta).

When is it ordered?

A CK test may be ordered whenever muscle damage is suspected and at regular intervals to monitor for continued damage. It may be ordered when someone has experienced physical trauma, such as crushing injuries or extensive burns. The test may be ordered when a person has symptoms associated with muscle injury such as muscle pain or weakness and when a person has nonspecific symptoms, especially when taking a drug or after an exposure to a substance that has been linked with potential muscle damage.

The CK test may sometimes be ordered when a person has chest pain and a heart attack is suspected. It may be ordered after a heart attack has been diagnosed to monitor for ongoing heart damage.

What does the test result mean?

A high CK, or one that goes up from the first to the second or later samples, generally indicates that there has been some recent muscle damage but will not indicate its location or cause. Serial test results that peak and then begin to drop indicate that new muscle damage has diminished, while increasing and persistent elevations suggest continued damage.

People may have CK levels that are significantly to greatly increased, depending upon muscle damage severity. Those who have rhabdomyolysis may have CK levels that are as much as 100 times normal levels.

Chest pain and increased CK levels indicate that it is likely that a person has recently had a heart attack. Levels that drop, then rise again may indicate a second heart attack and/or ongoing heart damage.

Normal CK levels may indicate that there has not been muscle damage or that it occurred several days prior to testing.

Moderately increased CK levels may be seen following strenuous exercise such as in weight lifting, contact sports, or long exercise sessions.

Complications can result from the rapid release of cell contents into the blood. This has been known to cause damage to kidneys (acute kidney injury, AKI) and disseminated intravascular coagulation (DIC). Once diagnosed and depending on the extent of injury, a person with rhabdomyolysis may be treated with intravenous fluids and other supportive care as well as procedures used to protect organs (e.g., dialysis to prevent/limit kidney damage).

3. Should everyone with muscle pain and weakness have a CK test?

Muscle pain and weakness are common symptoms that are seen with many temporary conditions. General, routine CK testing is usually not required. However, if someone is taking a drug or has been exposed to a substance that has been linked with potential muscle damage, then CK testing may be indicated.

4. Is there anything I can do to lower my CK level?

CK levels are a reflection of muscle damage. Temporary increases are seen with strenuous exercise but are not typically a concern unless severe or combined with extreme heat or humidity. An Increase in CK that is due to exposure to a toxin or a drug can be resolved by avoiding the toxin and/or potentially stopping taking the drug or changing it. You should not, however, stop taking a medication without first consulting with your doctor. Increases in CK that are due to an underlying disease, such as diabetes or hypothyroidism, may resolve by controlling the condition.

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Elsewhere On The Web

Article Sources

NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.

Schreiber, D. and Miller, S. (Updated 2011 March 29). Use of Cardiac Markers in the Emergency Department. [On-line information]. Available online at http://emedicine.medscape.com/article/811905-overview through http://emedicine.medscape.com. Accessed December 2012.

National Institute of Neurological Disorders and Stroke. NINDS Kennedy's Disease Information Page. Available online at http://www.ninds.nih.gov/disorders/kennedys/kennedys.htm through http://www.ninds.nih.gov. Accessed November 2014.

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This article was last reviewed on February 25, 2013. | This article was last modified on February 24, 2015.

The review date indicates when the article was last reviewed from beginning to end to ensure that it reflects the most current science. A review may not require any modifications to the article, so the two dates may not always agree.

The modified date indicates that one or more changes were made to the article. Such changes may or may not result from a full review of the article, so the two dates may not always agree.